SANTA CLARA -- The starters and top reserves are set at all but one position on the 49ers' defense.

Defensive coordinator Vic Fangio is still waiting for a safety not named Donte Whitner or Dashon Goldson to earn his confidence in the final two exhibition games.

"We've got some jobs that are up for grabs in the backup area," Fangio said Tuesday. "We'd like to see somebody step forward and make the decisions easy for us, particularly at the safety positions.

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"We know we have Whitner and Goldson. But we're looking to see who are our third, fourth and, possibly, fifth safety. We need for that to clear itself up. Hopefully, guys will step forward and make it easy. Right now, it hasn't been an easy decision for us there."

The candidates?

--C.J. Spillman has been the team's third safety through the entire offseason. Known as one of the top special-teams players in the NFL, Spillman has seen only limited time on defense in three previous seasons. He was used primarily in the 49ers' goal-line defense last year, playing just 16 snaps of defense in 16 regular-season games.

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--Darcel McBath enters his fourth NFL season after playing 20 games with the Denver Broncos in 2009 and '10, and one game last season for the Jacksonville Jaguars. "With the guys he's battling with, he does have more experience than all of them," Fangio said.

--Trenton Robinson was a sixth-round draft pick, who has showed slow and steady improvement, Fangio said. The 49ers would like to see a big spike in his play. He got turned around on a deep ball from Houston quarterback Matt Schaub to All-Pro receiver Andre Johnson on Saturday.

--Michael Thomas is an undrafted rookie from Stanford, who has not gotten much action at safety. He is seeing most of his action as a nickel back, the position from which he blitzed and picked up a sack against the Texans.

--Colin Jones, a second-year player, is a core special-teams player. He did not see any action at safety last season. He worked into the game Saturday for 10 snaps.

Or . . .

--NFL teams must trim to roster maximums of 75 on Aug. 27 and all the way down to 53 players on Aug. 31. The 49ers are sure to keep an eye on the waiver wire to see if there's a player available who might be able to lend assistance.